1. Technical Field
The present invention relates to a photo conductive antenna, a camera, an imaging apparatus, and a measurement apparatus.
2. Related Art
Recently, terahertz wave as electromagnetic wave having frequencies from 100 GHz to 30 THz has attracted attention. The terahertz wave may be used for imaging, various kinds of measurement including spectroscopic measurement, non-destructive test, etc., for example.
A terahertz wave generator that generates the terahertz wave has a light pulse generation unit that generates light pulse with a pulse width of about subpicoseconds (several hundreds of femtoseconds) and a photo conductive antenna (PCA) that generates terahertz wave by application of the light pulse generated by the light pulse generation unit, for example.
For example, Patent Document 1 (JP-A-2009-124437) has disclosed a photo conductive antenna including a semi-insulating GaAs substrate, a GaAs (LT-GaAs) layer formed by low-temperature MBE (molecular beam epitaxy) on the semi-insulating GaAs substrate, and a pair of electrodes formed on the LT-GaAs layer. Further, Patent Document 1 has disclosed that free carriers excited in the LT-GaAs layer are accelerated by an electric field of a bias voltage, a current flows, and terahertz wave is generated due to change of the current.
It is desirable that the strength of the terahertz wave generated in the photo conductive antenna is larger, and thereby, for example, an imaging apparatus and a measurement apparatus with higher detection sensitivity may be realized.
It is known that the strength of the terahertz wave generated in the photo conductive antenna depends on electron mobility (carrier mobility) of a receiving part of pulsed light in the photo conductive antenna. That is, the larger the carrier mobility of the receiving part, the higher the strength of the terahertz wave generated in the photo conductive antenna.
In the photo conductive antenna of Patent Document 1, the carrier mobility of the LT-GaAs layer is smaller, and it may be impossible to generate the terahertz wave with the higher strength or realize an imaging apparatus and a measurement apparatus with the higher detection sensitivity.